Polyhedral borane fogged direct-positive silver halide emulsion containing an organic sulfoxide

ABSTRACT

DIRECT POSITIVE PHOTOGRAPHIC SILVER HALIDE EMULSION ELEMENTS HAVING IMPROVED DEVELOPED SLVER COVERING POWER RESULTING IN INCREASED MAXIMUM DENSITY ARE PREPARED BY ADDING TO A CHEMICALLY FOGGED SILVR HALIDE EMULSION AT THE START OR DURING THE DIGESTION STEP FROM 50 TO 400 MILLILITERS OF A DIALKYL SULFOXIDE PER 1.5 MOLES OF SILVER NITRATE. THE ALKYL GROUPS OF THE SULFOXIDE MAY CONTAIN FROM 1 TO 4 CARBON ATOMS. THEE SILVER HALIDE EMULSIONS ARE PREFERABLY FOGGED WITH AMINE BORANES OR BORON HYDRIDES IN WHICH THE SKELETAL FRAMEWORK FORMS A POLYHEDRON BORANE CAGE CONTAINING 6 TO 12 BORON ATOMS OR A FRAGMENT THEREOF, THE WHICH MAY CONTAIN HETEROSKELETAL ATOMS SELECTED FROM THE GROUP CONSISTING CARBON, SULFUR AND NITROGEN ATOMS.

fULs. c1. sis- 107 POLYHEDRAL -BORANE FOGGED DIRECT-POSI- TIVE SILVERHALIDE EMULSION CONTAINING AN ORGANIC SULFOXIDE John H. Bigelow,Rochester, N.Y., assignor to E. I. du Pont de Nemours and Company,Wilmington, Del. No Drawing. Filed Feb. 15, 1972, Ser. No. 226,513 Int.Cl. G03c 1/28 15 Claims ABSTRACT on THE DISCLOSURE Direct positivephotographic silver halide emulsion elements having improved developedsilver covering power resulting in increased maximum density areprepared by adding to a chemically fogged silver halide emulsion at thestart or during the digestion step from 50 to 400'milliliter's of adialkyl sulfoxide per 1.5 moles of silver nitrate. The alkyl groups ofthe sulfoxide may contain from 1 to 4 carbon atoms. The silver halideemulsions are preferably fogged with amine boranes or boron hydrides inwhich the skeletal framework forms a polyhedron borane cage containing 6to 12 boron atoms or a fragment thereof, and which may containheteroskeletal atoms selected from the group consisting of carbon,sulfur and nitrogen atoms.

BACKGROUND OF THE INVENTION Field of the invention This invention.relates tordirect positive colloid silver halide photographic emulsions;more particularly it relates to such emulsions which are prefogged by achemical fogging agent. Still more particularly, it relates to directpositive emulsions chemically fogged by borane compounds havingincreased developed silver covering power over the prior art directpositive elements.

Description of the prior art Direct positive emulsions are of course,well known and there are many diiferent methods of producing directpositive images. For example, a silver halide emulsionmay be given ashort over-all exposure of high intensity radiation and then given alonger imagewise exposure of lower, intensity. Upon development, adirect positive will be obtained. Another method is to expose imagewiseand develop and bleach out developed silver, flash' expose and thenredevelop. A still further method is to use emulsion coated elementswhich have been chemicallyfogged with, for example, formaldehyde, hy-

idrazine, sodium arsenite, silver ions and other non-sulfide foggingagents thus eliminating a solarizing exposure. -Upon imagewise exposureand development of such Burt, U.S. Pat. 3,445,235. The Butt patentdiscloses and claims the use of rhodium and iridium salts in the directpositive emulsions described in the above Bigclow and Burtpatent asanti-kinking agents. The direct positive emulsions made as described inthe Bigelow and Burt patents are quite fast as compared to directpositive elements of the prior art and avoid many of the disadvantagesof long exposure times, low reversal densities, undesirable stain due todesensitizing dyes, as well as undesirable contrast, and a multiplicityof exposure steps United States Patent 3,782,959 Patented Jan. 1, 1974SUMMARY OF THE INVENTION It has now been found that the developed silvercovering power and maximum density of direct positive elements whichhave been chemically fogged, with at least one borane compound can besubstantially increased by the addition of organic sulfoxides which canbe represented by the following general formula:

wherein R and R are organic radicals which may be the same or differentand may be various alkyl or aryl groups, e.g., methyl, ethyl, propyl,butyl, phenyl, tolyl,

etc. The borane compounds may be selected from the amine boranes, andborane compounds in which a skeletal framework forms a polyhedron cageor a fragment thereof, and which may contain heteroskeletal atomsselected from the group consisting of carbon, sulfur and nitrogen atoms.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Among the borane compoundswhich have been found useful as chemical sensitizers in this inventionare the amine boranes disclosed in Bigelow and Burt, U.S. 3,361,- 564,e.g. morpholine borane, trimethylamine borane, etc., and boran hydridecompounds in which the skeletal framework forms a polyhedron or afragment thereof containing 6 to 12 boron atoms and may contain one ormore heteroskeletal atoms such as carbon, sulfur and nitrogen. In otherwords, the useful compounds may be polyhedral homonuclear boranes of theseries B H to B12H122 and the polyhedral heteronuclear boranescomprising the polyhedral azaboranes, polyhedral thiaboranes andpolyhedral carboranes. These boranes and their preparation are describedin The Chemistry of Boron and Its Compounds, E. L. Muetterties, JohnWiley and Sons, New York, 1967 Polyhedral Boranes, by E. L. Muettertiesand W. H. Knoth published by Marcel Dekker, Inc., New York, 1968 andnumerous patents by the authors of the above publications.

While in general dialkyl sulfoxides wherein the alkyl groups containing1 to 4 carbon atoms may be used it is preferred to use dimethyl ordiethyl sulfoxide. The sulfoxides are preferably added in the amount of50 to 400 milliliters per 1.5 moles of silver and at the beginning,during or at the end of the digestion period after the emulsion has beenwashed to remove the excess soluble salts resulting from theprecipitation of the silver halides. They may be added separately or inadmixture with the borane compounds and in the latter case the sulfoxidemay be used as the solvent for the borane compound as a convenient meansof adding it to the emulsion. The sulfoxides may be prepared by themethods disclosed in Smedslund, U.S. Pat. 2,702,824 and Goheen et al.,U.S. Pat. 2,925,442.

For most efficient fogging action it is preferred that the boranecompounds be added during the same stage as the sulfoxide compounds. ThepH of the emulsion is adjusted to between 3.0 and 9.0 and preferablybetween 3.0 and 7.0 and maintained at a pre-selected level in this rangeduring digestion. After digestion, the pH is adjusted to the desiredcoating pH and the conventional coating aids are added. Coating aidssuch as saponin, sodium salts of polyether sulfonates, alkyl sulfonates,cetyl betaine, etc., can be utilized. The emulsion is then coated anddried in the manner known to those skilled in photographic manufacturingmethods.

The sensitometric characteristics of the direct positive emulsions maybe determined by exposing in an intensity scale sensitometer (describedon p. 616, Mees, The Theory of the Photographic Process, MacMillanCompany, New York (1942)) using a suitable step wedge and lightintensity depending upon the inherent speed of the emulsion. Directpositive emulsions are of course tailored to meet certain needs in theindustry and are manufactured accordingly. After exposure in thesensitometer the strips are developed in suitable developers as shownbelow, immersed in a short stop, fixed in a conventional fixer, washedand dried. In evaluation of the processed strips, the maximum density isthe highest density value obtained on the image of the step wedge andcan be Developer I (high contrast type):

Water m1 500 Sodium sulfite (anhydrous) grams 30.0 Paraformaldehyde do7.5 Potassium metabisulfite d 2.5 Boric acid (crystals) do.. 7.5Hydroquinone do 22.5 Potassium bromide do 1.5 Water to make 1.0 liter.

Developer II (continuous tone type):

Water ml 500 N-methyl-p-aminophenol sulfate grams 1.0 Sodium sulfite(anhydrous) ..do 15.0 Hydroquinone do 4.0 Sodium carbonate (monohydrate)do.. 26.5 Benzotriazole d0.. 0.1 Potassium bromide do.. 0.6

'Water to make 1.0 liter. Sensitometric evaluation adduced the followingdata:

Amount of dimethyl sulfoxide per 1.5 Coating Maximum density Boranecompound mole/1.5 moles moles weight, mg.

AgNOa AgNOg, ml. AgNQs/t't. Dev. I Dev. II

Morpholino borane 4. 8 1O 1 None 512 3.61 3. 71 0518 11123.-. 3. 6X10- 1None 861 4.17 4. 25 CSB9H zS 0.9 10 1 None 615 4. 45 4.55 CSBQHIQS 4.5X10- 1 None 850 4. 35 4. 25 Morpholine borane 4. 8X10- 360 444 3. 87 4.85 C H BHHNS 3. 6X16 360 709 5. 99 6. 85 CQHjfiBllHlOS 2X10 200 779 6.73 6. 85 OGHsBllHlOS 1 10- 100 619 5. 63 5. 45 (CIIs)4NB1oHu 3. 6Xl0'360 726 6. 65 6.85 (CH3)4NB10H11S ZXIO- 200 674 7. 15 7.05 (CHshNBioHnS-1 10- 160 657 6. 05 6.13 CSBpHlzS 0. 9X10 120 l, 301 6. 85 7. 15+CSBQHUS 3. 6X10 360 840 7. 15+ 7. 15+

1 Control.

consldered a measure of the effect of the addition of the EXAMPLE IIsulfoxide compound to the system.

The invention will now be illustrated in and by the following examples:

EXAMPLE I A direct positive emulsion was made in the following manner.To an aqueous solution of gelatin containing 1 mole of potassiumchloride and 6.8 mole of rhodium trichloride, there was rapidly added 1mole of silver nitrate in an aqueous solution. To the resulting mixturethere was added 0.4 mole of potassium bromide in aqueous solution andthe resulting emulsion was then ripened by heating for 10 minutes at 160F. A second portion of 0.6 mole of potassium bromide was added and theemulsion further ripened 10 minutes at 160 F. The resulting emulsion wasthen cooled, washed and redispersed in the manner disclosed in Moede,U.S. Pat. 2,772,- 165, issued Nov. 27, 1956.

The aqueous gelatin solution was added to the redispersed emulsion toprovide a gelatin content of about 7 to 8%. The pH was adjusted to 8.2and borane compounds and dimethyl sulfoxide were added to separateportions of the emulsion in the quantities indicated in the followingtable. The emulsions were stirred and digested for 40 minutes at 130 F.The emulsions were cooled to 95 F. and the pH adjusted to 7.0 withacetic acid and a wetting agent, i.e., saponin, was added. The viscositywas suitably adjusted and the emulsion was coated at approximately 700mg. AgNO per square foot on a photographic film support and dried in aconventional manner. Sensitometric strips were exposed in the abovedescribed sensitometer with a quartz-I lamp, /3 wedge, and luxometerunits. The strips were developed in the two following developers, 3minutes in the developer I and 1.5 minutes in developer II.

A direct positive emulsion was made as described in Example I up to andthrough the washing and redispersion steps. The temperature of theredispersed emulsion was raised to 130 F. and there was added an aqueoussolution of gelatin to give a final concentration of 7 to 8% gelatin.The pH was adjusted to 7.0 and 4.0 10- mole of the borane compound CsB HS and 7.4 10- mole of hydrochlorauric acid (HAuCl per 1.5 moles ofsilver nitrate was added. The emulsion was divided into two portions thequantities of dimethyl sulfoxide as indicated in the table 'below. Theemulsions were digested for 40 minutes at 130 F. and cooled to F. Theusual coating aids, e.g. wetting agents, emulsion hardeners, etc. wereadded and the emulsions were coated on photographic quality film baseand dried in a conventional manner. Strips of the exposed emulsionelements were exposed in the intensity scale sensitometer referred toabove using a #3 lamp, SQRTZ wedge Ser. No. 8,876,418 for 16 seconds.The strips were processed as described in Example I and gave thefollowing data:

Maximum density Amount of dimethyl sulioXide/LB AgNOa Dev. I Dev. II

while others, particularly the amine boranes operate more effectivelyabove 7 and preferably 8.0 to 9.0.

As is evident from the sensitometric data, the use of dialkyl sulfoxideswith the borane fogging agents increases the maximum density of thedirect positive elements. The elements of this invention, as shown inthe examples, may be developed in any standard developing solutioneither of the continuous tone type or the high contrast lithographictype using standard techniques. Variations in the developing solutionwill have much the same eifect as it would in developing non-reversalemulsions. No pre-exposure operations or auxiliary processing proceduresare necessary or desired in using the novel elements of this invention.It is also unnecessary to utilize stain producing non-sensitizing dyesor other desensitizing compounds in the emulsion. The borane compoundsare far superior to formaldehyde, the principal fogging agent of theprior art, because the boranes do not have a hardening effect on thegelatin layer.

The silver halide emulsions of this invention can be made with any ofthe macromolecular, water-permeable colloids known to be suitable forthe purpose of acting as a colloid carrier for silver halide grains. Inaddition to gelatin, there may be used polyvinyl alcohol and itsderivatives, e.g., partially hydrolyzed polyvinyl acetates, ethers andacetals, hydrolyzed interpolymers of vinyl acetate and unsaturatedaddition polymerizable compounds such as maleic anhydride, acrylic andmethacrylic acid esters, poly-N-vinyllactams, polysaccharides, e.g.,dextran, dextrin, etc., the hydrophilic copolymers disclosed inShacklett US. 2,833,650, hydrophilic cellulose ethers and esters, andacrylamide polymers. Mixtures of these binders can also be used as wellas water-permeable binding agents containing dispersed polymerized vinylcompounds such as those disclosed in Nottorf US. Pat. 3,142,568 issuedJuly 28, 1964.

The emulsions of this invention may be coated on any suitable supportincluding photographic quality paper and transparent film. For example,the cellulosic supports, e.g., cellulose acetate, cellulose triacetate,cellulose mixed esters, etc., may be used. Polymerized vinyl compounds,e.g., copolymerized vinyl acetate and vinyl chloride, polystyrene andpolymerized acrylates may also be mentioned. The film formed from thepolyesters made according to the teachings of Alles, US. Pat. 2,779,684and the patents referred to in the specification of that patent. Othersuitable supports are the polyethylene terephthalate/isophthalates ofBritish Pat. No. 766,290 and Canadian Pat. 562,672 and those obtainableby condensing terephthalic acid and dimethyl terephthalate withpropylene glycol, dimethylene glycol, tetramethylene glycol orcyclohexane-1,4-dimethanol(hexahydro-pxylene alcohol). The films ofBauer et al., U.S. Pat. 3,059,543 may also be used. The above polyesterfilms are particularly suitable because of their dimensional stability.The emulsions are generally coated on the supports to give a coatingweight equivalent to about 700 mg./ft.

Many borane compounds other than those referred to above can be used aschemical fogging agents for the direct positive photographic elements ofthis emulsion in accordance with this invention.

What is claimed is:

1. A direct-positive, water-permeable colloid-silver halide emulsioncontaining a fogging amount of a borane and an organic sulfoxide of theformula wherein R and R are phenyl and tolyl and alkyl radicalscontaining 1 to 4 carbon atoms, said borane being selected from thegroup consisting of the amine boranes and the boron hydrides, said amineboranes and boron hydrides having a polyhedral skeletal framework whichhas from 6 to 12 carbon atoms and may contain heteroskeletal atomsselected from the group consisting of carbon, sulfur and nitrogen.

2. An emulsion according to claim 1 wherein said organic sulfoxide isdimethyl or diethyl sulfoxide.

3. An emulsion according to claim 1 wherein said organic sulfoxide ispresent in an amount of 50 to 400 milliliters per 1.5 moles of silver.

4. An emulsion according to claim 3 containing rhodium chloride.

5. An emulsion according to claim 3 wherein the silver halide is asilver chlorobromide emulsion.

6. An emulsion according to claim 3 wherein the silver halide is asilver bromochloride emulsion.

7. An emulsion according to claim 3 wherein the colloid is gelatin.

8. An emulsion according to claim 3 wherein said boron hydride is apolyhedral homonuclear borane of the series B6H6 2 t0 B zHlg 9. Anemulsion according to claim 3 containing a gold compound.

10. An emulsion according to claim 3 having a pH of about 3.0 to 9.0.

11. A photographic element comprising a support bearing a layer of anemulsion as defined in claim 1.

12. An element according to claim 10 wherein said organic sulfoxide isdimethyl or diethyl sulfoxide.

13. An element according to claim 11 wherein said organic sulfoxide ispresent in an amount of 50 to 400 milliliters per 1.5 moles of silver.

14. An element according to claim 13 containing rhodium chloride.

15. An element according to claim 12 containing a gold compound.

References Cited UNITED STATES PATENTS 3,219,450 11/1965 Goldberg 96-1073,607,288 9/1971 Burt 96-64 NORMAN G. TORCHIN, Primary Examiner W. H.LOUIE, JR., Assistant Examiner US. Cl. X.R. 96l08

